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Pampadromaeus, Bridging the Theropod – Phytodinosaur Transition

Pampadromaeus barberenai
Pampadromaeus barberenai (Cabriera et al. 2011) is a new dinosaur from the Late Triassic of Brazil. It was originally described as a stem sauropodomorph known from a partial disarticulated skeleton and most of the skull bones. The authors reported, “Based on four phylogenetic analyses, the new dinosaur fits consistently on the sauropodomorph stem, but lacks several typical features of sauropodomorphs, showing dinosaur plesiomorphies together with some neotheropod traits.”

Figure 1. Pampadromaeus in left lateral view. The skeleton was disarticulated and semi-complete.

Pampadromaeus was small (slightly longer than a meter in length) biped with a generalized basal dinosaur morphology, not quite a theropod and not quite a phytodinosaur (sauropods + ornithisuchians + pseudornithisichians).

Figure 2. The skull of Pampadromaeus as it was originally reconstructed. Upper left: The skull of Eoraptor for comparison. To the left, images of the premaxilla and maxilla restored. Note the length of the premaxillary teeth and their proximal exposure. The newly mated premaxilla does not descend so much as in the original reconstruction.

Generalized Morphologies Generally Make for Great Transitional Taxa
Cabriera et al. (2011) added Pampadromaeus to four prior studies and in each case Pampadromaeus nested as a sister to Sauropodomorpha or as a sister to Saturnalia + Sauropodomorpha. Only ten taxa were included in each test. In each study Silesaurus + Ornithischia were outgroup taxa.

I added just the skull elements to the large reptile study (Fig. 3) and found it nested between members of the Theropoda and the Phytodinosauria, basal to its basalmost member, Daemonosaurus. Daemonosaurus was not included in the Cabriera et al. (2011) study based on prior studies. This nesting agrees with the Cabriera et al. (2011) results, but the expansion of the taxon list (Fig. 3) sheds more light on the nesting of this new and phylogenetically important dinosaur.

Figure 3. A portion of the large reptile tree indicating the nesting site of Pampadromaeus. Click to see the entire tree.

This is an Important GenusPampadromaeus is a key taxon linking theropods to all other dinosaurs, the herbivorous Phytodinosauria via Daemonosaurus. The enlargement of the premaxillary teeth observed in Daemonosaurus has its genesis in Pampadromaeus. The torso was shorter than in Saturnalia. The ilium resembled that of Herrerasaurus and Sanjuansaurus. The dorsal spines were lower than in Herrerasaurus. More detailed comparison can be found in Cabriera et al. (2011).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.